Datasheet

STPMC1 Theory of operation
Doc ID 15728 Rev 7 29/77
Where:
I
max
= 2
16
Σ I
X
= I
R
+ I
S
+ I
T
+ I
N
for SYS = 0, 1, 2, 3, 4, 7
Σ I
X
= I
S
+ I
T
for SYS = 5, 6
Bit
BCS is set according to Ta bl e 1 5
with (Σ i
X
)
RMS
= (i
R
+ i
S
+ i
T
+ i
N
)
RMS
Example 5: 3-ph system - BCS = 0
Let us consider a three-phase, four wires system where the RMS values of the current
applied are:
I
R
= 5 A
I
S
= 5 A
I
T
= 4.4 A
I
N
= 0 A
The sum of all instantaneous currents (i
R
+ i
S
+ i
T
+ i
N
) should always be zero, unless
there is a tamper condition.
The STPMC1 calculates this sum and put its RMS value divided by four (called sIRMS)
into register DMN (see paragraph
9.17.2 ).
This value should always be zero (or very close).
In our case:
The currents are shown in
Figure 11 below.
∑
>
256
I
I
max
X
Table 15. Tamper conditions
BCS SYS = 0, 1, 2, 3, 4, 7 SYS = 5, 6
0
or
or
1 or
()
8
I
i
X
RMS
X
∑
∑
<
STS
I
7
9
II
9
7
<<
TST
I
7
9
II
9
7
<<
()
8
I
i
X
RMS
X
∑
∑
>
STS
I
7
9
II
9
7
>>
TST
I
7
9
II
9
7
>>
A149967.0
4
i
sIRMS
RMS
X
=
⎟
⎠
⎞
⎜
⎝
⎛
=
∑